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Mechanical properties of dental biomaterials 2
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To Compare the properties of two materials:
Elastic Modulus of material (A) is higher than that of material (B)Elastic Modulus of material (A) is higher than that of material (B)
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#Strength = Height of the curve
#Stiffness (Rigidity) = Slope of the curve
A
A
B
B
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#Ductility & Flexibility
A B
X Y Z X Y Z
X Y Z X Y Z
# Resilience & Toughness = Area under the curve
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#Ductility & Flexibility
A B
X Y Z X Y Z
X Y Z X Y Z
# Resilience & Toughness = Area under the curve
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Question?
• Is rubber a rigid or a flexible material?
• Which is stronger? Glasswaxstainless steel
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Testing compressive strength of a material:
• Specimen shape: Cylindrical
• Type of force used: compression
•Tester: Universal Testing Machine
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Tensile strength testing:
• Specimen shape: Dumble-shape
• Type of force: Tension
• Tester: Universal Testing Machine
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Brittle materials: They are materials which
undergo fracture or rupture with little or no prior permanent deformation.
They are stronger under compression rather than tension.
Their tensile strength can be calculated using:
Diametral compression test. (Indirect tensile test)
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Fig 15: A drawing to illustrate how compression force develops tensile stress in brittle material
Fig 15: A drawing to illustrate how compression force develops tensile stress in brittle material
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Diametral compression test of brittle materials:
• Specimen shape: Disk-shaped
• Type of force applied: Compression
• Resultant force: Tension
• Tester: Universal Testing Machine
Stress = 2P Load π D T Diameter X Thickness
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Compression
Tension
Shear
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Transverse strength - Modulus of Rupture:(3 point bending test)
It is the ability of a material to bend before it breaks.
Stress= 3 Load X Length
2 X Width X Thickness2
Strain= Load X Length3
4 Elastic Modulus X Width X Thickness3
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Fig 16-a: Diagrammatic representation of a 3-point bending test or transverse test bending of the beam introduces both
tensile and compressive stresses.
Fig 16-a: Diagrammatic representation of a 3-point bending test or transverse test bending of the beam introduces both
tensile and compressive stresses.
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Impact strength
Materials such as glasses,
ceramics, cements and amalgam
have low resistance to breakage
when a load is applied by
impact. (dynamic load).
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Denture mid-line fracture Porcelain bridge fracture
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The impact strength is defined
as the energy required to
fracture a material under an
impact force.
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Impact strength (Charpy tester)
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Hardness:
It is defined as the resistance of a material to surface penetration or indentation.
There are four common standard test methods for expressing the hardness of a material: Brinell, Rockwell, Vickers, and Knoop.
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HARDNESS
The property of hardness is of major
importance in the comparison of
restorative materials.
Hardness is defined as to resistance
to permanent surface indentation or
penetration.
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1. Brinell hardness test• Shape of indentor: Sphere• Indentor material: Tungestun or carbide• Size of indentor: 1.6 mm in diameter•Type of indentor: Macro-indentor• Measurement: Depth of indentation
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2. Rockwell hardness test• Shape of indentor: Cone shaped• Indentor material: Tungestun or carbide• Size of indentor: 1.6 mm in diameter•Type of indentor: Macro-indentor• Measurement: Depth of indentation
Limitation:Can not be used to test the hardness of brittle materials.
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3. Vickers Hardness Test
• Shape of indentor: Pyramid-shaped• Indentor material: 136 degree Pyramid• Type of indentor: Micro-indentor• Measurement: Diagonal of indentation
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4. Knoop hardness test
• Shape of indentor: Pyramid-shaped• Indentor material: Diamond• Type of indentor: Micro-indentor• Measurement: The longer diagonal of indentation.
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Shore A test• Shape of indentor: Blunt pointed• Indentor material: Steel• Type of indentor: For rubber materials.• Measurement: The depth of indentation.
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Why do we need to know the mechanical properties of the materials? Human Dentin
Density 2.1 ~ 2.2E-9 Mg/mm3Modulus of Elasticity 12 ~ 14000 MPaYield Stress 240 MPa
Cementing Agents – Zinc PhosphateDensity 3.94E- 09 Mg/mm3Modulus of Elasticity 13400 MPaYield Stress 6.9 MPa
Aluminum OxideDensity 3.72E- 09 Mg/mm3Modulus of Elasticity 14000 MPaYield Stress 352 MPa
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